It can actually be very tricky to define a species, but in the 1900s, scientists found a pretty good way.

If you went to Mars, you’d need to be able to survive an extremely punishing environment. This picture, taken by NASA’s Mars Exploration Rover Opportunity, gives you an idea.
NASA/JPL-Caltech/Cornell Univ./Arizona State Univ. 26 novembre 2018

The energy needed to pull magnets apart comes from you, and you get it from the food you eat. And the plants or animals you eat get their energy from other plants and animals, or from the Sun. All energy comes from somewhere.

Dropping leaves might seem like a waste, but plants are actually saving nutrients.

The composition of black and white in a magpie’s poo differs between species. Some splatter more of the uric acid (white), some have more black (indigestible solids). It depends on their diet.
Gisela Kaplan24 octobre 2018